This simian immunodeficiency virus (SIV) vaccine trial was based on a combination immunization protocol with recombinant vaccinia virus containing SIV glycoproteins, gp160 or gp120. Booster immunizations were done using baculovirus-SIV gp120, vaccinia-SIV gp120 or CHO-SIVgp120. Viral challenge was performed using SIVmac239(nef followed by rechallenge with SIVmac251. When all vaccinated animals are compared with unvaccinated animals, there appears to be a general pattern of increased survival for the group of animals that received a vaccine. Of the seven unvaccinated control animals that were held throughout the study, all developed AIDS rapidly, i.e., within 32-107 weeks. In contrast, only eight of thirteen (62%) vaccinated animals have developed AIDS to date and four remain healthy, although viremic. In addition, the average survival time for the unvaccinated group was 56 weeks, whereas the vaccinated group averages greater than 3 years of survival. All long-term s urvi vors (>2 years) received a vaccine and had low levels of virus in their blood, suggesting that the vaccine may have a beneficial effect. These data suggest that HIV recombinant vaccines containing viral glycoproteins should be investigated further for effectiveness against HIV infections. FUNDING NIH grant RR00166 and NIH-NIAID contract AI65302. Grant, R.F., Coon, E.M., Agy, M.B., Miller, N., Giavedoni, L., Jones, L., Ahmad, S., Yilma, T., and Morton, W.R. Prolonged survival associated with low viral loads in vaccinated rhesus macaques challenged with SIVmac. J. Med. Primatol. 27 abstract #41, 1998.